Characterization of the synthesis and release of human placental lactogen and human chorionic gonadotropin by an enriched population of dispersed placental cells.

An enriched fraction of human placental cells that synthesize and release both placental lactogen (hPL) and hCG was obtained by isopycnic centrifugation of collagenase/hyaluronidase-dispersed cells through a density gradient of 40% Percoll. The enriched cells, which banded at a density of approximately 1.01 g/ml, comprised 10-15% of the total DNA. During the first 24 h after attachment, the cells released 50-250 ng hPL and 4-10 mIU hCG/10(6) cells. Thereafter, the rate of hPL release decreased, while the rate of hCG and [35S]trichloroacetic acid-precipitable protein release remained constant. The enriched cells responded to phospholipase A2, low extracellular calcium, and (Bu)2cAMP in a manner similar to that of placental explants. Phospholipase A2 (0.1 and 1 U/ml) stimulated hPL release by 270% and 568%, respectively, and low extracellular calcium (0-0.18 mM) stimulated hPL release by 48%. (Bu)2 cAMP (1 mM) stimulated hCG release by 42%, but had no effect on hPL. Estradiol (10(-5)-10(-12) M) and progesterone (10(-5)-10(-10) M) had no effect on the synthesis and release of either hPL or hCG over a 6-day period. In addition, insulin (8.3 X 10(-7) M) and changes in medium glucose content (0-5 mg/ml) had no effect on hPL release over a 72-h period. Since the enriched trophoblast cells respond to provocative stimuli in a manner similar to that of explants and placental fragments, this cell population is a useful model system for investigations of the cellular mechanisms of hPL and hCG release.